Generally, pressure swing adsorption or PSA is used to increase the concentration of a selected gas from a mixture of gases. In particular, an oxygen concentrator, for example for medical or therapeutic use, increases oxygen concentrations from ambient air to therapeutic levels for inhalation by a patient. One such PSA oxygen concentrator is the successful portable oxygen concentrator distributed by AirSep Corporation of Buffalo, N.Y. under the trademark LIFESTYLE, the principles of which are described in co-pending U.S. patent application No. 10/762,671, filed Jan. 22, 2004, which is a continuation application of an application on which U.S. Pat. No. 6,764,534, McCombs et al, issued Jul. 20, 2004. The entire disclosures of both the co-pending application and the patent are incorporated by reference. Because of its very compact size, a concentrator made as described is particularly attractive for use by patients who want to be highly mobile and yet be able to use the same device while inactive or asleep. Oxygen concentrators have significant advantages for patient use over other common oxygen sources such as liquid or pressurized gaseous oxygen tanks. However, because oxygen concentrators by their very nature move substantial volumes of ambient air, product gas and waste gases, they necessarily can generate levels of noise that may be less desirable in certain uses and environments. To counter that problem, I have developed novel and useful sound enclosures that will substantially reduce even further the emitted noise while at the same time not affect the operation or efficiency of the concentrators.